1

Loran Timing

ILA – 36th Convention and Technical SymposiumOrlando, Fl., Oct 16-17 2007

Arthur HelwigGerard Offermans

Christian Farrow

Outline

•Timing and Frequency use•Developing High-end Loran-C timing equipment (recap)

•Developing Low-end Loran-C timing equipment–Low-cost oscillator characterizaton–Received signal–Combining the two

•Conclusions

Outline

TimingFrequency

Time andFrequency

Receiver outputs:• 10 MHz• 2.048 MHz• 1.544 MHz

Necessary input:• eLoran/Loran-C signal

Receiver outputs:Frequency outputs, plus:• 1 PPS (aligned to UTC)• 10 PPS• 100 PPS• Serial output for

Time of Day message

Necessary inputs:• eLoran signal• Data channel for UTC

information

MTIE / TDEV

Relevant measurements:• MTIE

–Maximum Time Interval Error (MTIE): The maximum peak-to-peak delay variation of a given timing signal with respect to an ideal timing signal within an observation time τnτ for all observation times of that length within the measurement period (Τ).

• TDEV–Time Deviation (TDEV or σx(τ)): A measure of

the expected time variation of a signal as a function of integration time. TDEV can also provide information about the spectral content of the phase (or time) noise of a signal. TDEV is in units of time.

ETSI – EN 300 462- 3 - 1

ETSI EN 300 462-3-1 V1.1.1 (1998-05)

Transmission and Multiplexing (TM);Generic requirements for synchronization networks;Part 3-1: The control of jitter and wander withinsynchronization networks

• 864 ns / day• ASF fluctuations

not a problem

Loradd UTC series

• All functionalities of a normal LORADD receiver• Ovenized crystal for improved stability and hold-over (SRS SC10)• 10 MHz, 2.048 MHz and 1.544 MHz outputs• 1 PPS (Loran-C derived) output• 1 PPS (GPS derived) output• Loran-C Timing Source Station selectable

Test results - MTIE

ETSI PRC Mask

Loradd UTC performance10 ns

Test results - TDEV

ETSI PRC Mask

Loradd UTC performance

Low-cost

•Market demand for low-cost frequency-only receiver

•Frequency lock to a single Loran station

•No hold-over required

•Low-cost oscillator means shorter integration of received Loran signals

•Loradd-F•Low-cost VCO

•No GPS•10 MHz output via SMA

Loradd-F

Low-cost oscillator characterization

• Crystal oscillator frequency varies

• Graph displays frequency vs time

• Receiver operating at room temperature

• After warming up for several days

• Most likely still due to temperature variations

Free-running VCO

Time (s)

Fre

quen

cy e

rror

(ns

/s)

200 s

4e-10

Low-cost oscillator characterization

Time interval: 200sFrequency error: 4e-10Phase error (over 200 s): 40 ns

MTIE mask: 25 ns

When left uncorrected, MTIEmask is broken at this point.

Free-running VCO

Time (s)

Fre

quen

cy e

rror

(ns

/s)

Received signal characterization

Rugby (6731Y)

5-second independent measurements

6731Y std=10.44 ns

TOA of Rugby (6731Y) @ Reeuwijk (408 km)

Time (s)

Mea

sure

d T

OA

(ns

)

Received signal characterization

Rugby (6731Y)

5-second independent measurements with 3-point moving median filter

6731Y std=8.18 ns

Transmitters are currently broadcasting in

a 10ns “grid”200 s

TOA of Rugby (6731Y) @ Reeuwijk (408 km)

Time (s)

Mea

sure

d T

OA

(ns

)

Combining the two

Low-quality VCO Loran TOA

MTIE MTIE

Combining the two

Low-quality VCO Simulated Loran TOA (σ=3.5 ns)No timing steps

MTIE MTIE

Conclusions

•Loradd UTC with high quality VCO fully meets MTIE specification

•Loradd-F with low-quality VCO does not yet meet MTE spec at 25<τ<110 s–Temperature controlled VCO–Higher grade VCO

•Timing steps in transmitter need to be investigated. Elimination will result in reduced cost receivers.